It’s the most effective way to do SEO. Unless you don’t do it correctly.
If you listen to Grumpy SEO Guy episodes 3-5 I walk you through the steps of how to do it.
Most PBNs are made from expired domains. Because the remaining choice is to start with new domains and build up their authority, which costs money and time.
So you either pay more for domains that have authority, or you pay less for domains that don’t have authority and then use money to get authority.
Do you want domains with authority now, or do you want domains with authority in 20 months?